The present invention relates to methods and apparatus for polishing substrates using chemical mechanical polishing (CMP).
CMP is one accepted method of planarization (controlled polishing) of substrates used in, for example, semiconductor fabrication. The existing CMP methods typically require that the substrate be mounted on a carrier or polishing head. An exposed surface of the substrate is placed against a rotating polishing pad, which may be a standard pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including a chemically-reactive agent (and abrasive particles if a standard pad is used) is applied to the surface of the polishing pad.
The CMP process provides a high polishing rate and a resulting substrate surface that is free from small-scale roughness and flat (lacking large-scale topography). The polishing rate, finish and flatness are determined by characteristics of the pad and slurry combination, the relative speed of the pad over the substrate, and the force pressing the substrate against the pad.
An existing rotating-belt type CMP processing apparatus 20 is illustrated in U.S. Patent Publication No. 2004/0209559, the entire disclosure of which is hereby incorporated by reference. A rectangular platen 100 includes a polishing sheet 110 that advances via rollers over a top surface 140 of the platen 100. A carrier head 80 receives a substrate 10 for polishing, and applies a downward pressure of the substrate 10 against the polishing sheet 110. A fluid may be injected between a top surface 140 of the platen 100 and the polishing sheet 110 to create a fluid bearing therebetween. In addition to the information contained in U.S. Patent Publication No. 2004/0209559, further details as to the structure of the carrier head 80 may be found in U.S. Pat. No. 6,183,354, the entire disclosure of which is hereby incorporated by reference.
An aperture or hole 154 may be formed in the top surface 140 of the platen 100 and aligned with a transparent strip 118 in the polishing sheet 110. The aperture 154 and transparent strip 118 are positioned such that they permit a “view” of the substrate 10 during a portion of the platen's rotation. An optical monitoring system 90 includes a light source 94, such as a laser, and a detector 96. The light source generates a light beam 92 which propagates through aperture 154 and transparent strip 118 to impinge upon the exposed surface of substrate 10. The apparatus 20 uses the optical monitoring system 90 to determine the thickness of the substrate 10, to determine the amount of material removed from the substrate 10, or to determine when the surface has become planarized. A computer 280 may be programmed to activate the light source 94 when the substrate 10 overlies the aperture 154, to store measurements from the detector 96, to display the measurements on an output device 98, and to detect the polishing endpoint. In addition to the information contained in U.S. Patent Publication No. 2004/0209559, further details as to the structure of the optical monitoring system 90 and computer 280 may be found in U.S. Pat. No. 5,893,796, the entire disclosure of which is hereby incorporated by reference.
One of the problems with the aforementioned rotating-belt type CMP processing apparatus is that there is not adequate control over the amount and quality of the pressure between the substrate being polished and the rotating polishing sheet. Accordingly, there are needs in the art for new methods and apparatus for polishing via CMP which result in improved substrate finishes.